11 TRVs and re-fill the system with Fernox F00079, which came in at £355.
The question is, is this a reasonable quote, or should I attempt it myself? My only worry is that it is a sealed system (not combi boiler though) and I wouldn't have a clue about where to add the inhibitor! I also know what my wife would say if I turned up with 11 valves in a bag and told her what I planned.
IMHO this is on the steep side. To DIY would cost you around £120. Its not more than a days work by any stretch of the imagination. The £120 figure also includes very high quality TRV`s and not junk which BG may or may not be fitting. Sealed systems are also far easier to fill and empty than your typical open vented. Just find the drain c*ck and open it. Then open all your bleed screws (upstairs first). Change all the valves and tails. To add the fernox, simply close the lockshield valve and TRV on a small radiator and disconect it from the pipes, then open one of the valves with radiator upside down and pour the fernox in. Then close both valves and put it back on wall. Reconnect to pipes and away you go. Close all bleed valves, refill and bleed system and finally check the pressure is correct.
Job done. :-)
Regards
John